Means for regulating the transmission over four-wire circuits



S. P. SHACKLETON.

MEANS FOR REGULATING THE TRANSMISSION OVER FOUR-WIRE CIRCUITS.

APPLICATION FILED SEPT. 10, 19H]. 1,438,270.

ATTORNEY 2 SHEETSSHEH l- S. P. SHACKLETON.

MEANS 'FOR REGULATING THE TRANSMISSION OVER FOUR-WIRE CIRCUITS.

APPLIFIATION FILED SEPT. 10, 1918.

Patented-Dec. 12, 1922.

2 SHEETSSHEE1 2.

- nun I'NVENOR.

ATTORNEY Patented Dec. 12, 1922.

nnira:

SAMUEL P. SHACKLETON, OF NEW YORK, N. Y., ASSIGNOR TO AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORKL MEANS FOR REGULATING THE TRANSMISSION OVER FOUR-WIRE CIRCUITS.

Application filed September 10, 1918. Serial No. 253,460.

To all whom it may concern:

Be it known that I. SAMUEL P. SHACKLE TON, residing at New York, in the borough 'of Bronx and State of New York, have invented certain Improvements in Means for Regulating the Transmission Over Four- Vire Circuits, of which the following is a specification.

This invention relates to transmission circuits, and more particularly to transmission circuits of the type known as four-wire circuits, although it is in general applicable to transmission circuits of any type.

The principal object of the invention is to provide suitable means for maintaining the transmission equivalent of a circuit constant, regardless of variations in the conditions affecting the electrical characteristics of the circuit. Other and further objects will, however, be clear from the description of the invention Hereafter appearing.

In general, the transmission equivalent of a circuit varies, due to a number of different causes. If the transmission circuit be of the four-wire type, in which apair of separate transmission lines are employed for transmission in opposite directions, these causes may be divided into two classes: The first class comprises causes .which affect both sides of the circuit, or in other words, both transmission 'lines, in the same manner. Among these auses may be enumerated variations in resistance of the conductors or loading coils, variations in the capacity, in ductance, or other electrical characteristics of the cable, and variations in the potential of repeater batteries common to repeaters in both sides of the circuit. The second class comprises causes which affect the two sides differently, such as variations in the structure of repeater bulbs where vacuum tube repeaters are employed, variations in the potentials of grid batteries, or accidental variations due to the resistance of bad joints, leakage due to poor insulation etc.

In the case of transmission circuits in which only one transmission line is used for transmission in the two directions. the fac-.

tor of variation in the two sides of the. circuit will be absent. but some or all of the above causes may contribute to produce variations in the transmission equivalent of the circuit, thereby rendering it highly desirable that some provision be made for overcoming the effects of these variations.

The present invention contemplates elimi.

nating arrangements, and interconnecting the ends through adjustable transmission devices having a' transmission equivalent double and opposite in sign to, that to which the sides of the four-wirecircuit exclusive of the terminals are to be adjusted. The gain in the four-wire circuit is then increased to a maximum value, preferably by increasing the amplification of one-way repeaters in the two transmission lines of the four-Wire circuit. This causes, singing to take place in the four-wire circuit and by gradually decreasing the amplification of similar amplifiers in the two transmission lines until singing just ceases the four-wire circuit will be set for the desired transmission equivalent. In order to perform these functions automatically the circuit may be so arranged that when the two ends'of the four-wire circuit are interconnected, an automatic switch controlling the setting of the potentiometers which determine the amplification of the repeaters, will be restored to its normal condition, thereby setting the potentiometers to permit the greatest possible amplification. Singing then takes place and an alternating current relay responsive to the singing oscillations may be arranged to control the advancing of the switch until the potentiometers are at a position such that singing just ceases.

The invention may now be more fully understood from the following description when read in connection with the accompanying drawings, Figure 1 of which is a diagram of a circuit arrangement embodying one form of the invention, while Figure 2 is anircuit diagram of a preferred form of the invention.

Referring to Figure 1, the four-wire circuit is shown interconnecting two ,distant stations C and D, said four-wire circuit comprising a pair of transmission lines L and L, for transmission in opposite directions. Normally the four-wire circuit is connected to terminating two-Wire lines L, and L at stations C and D respectively, through the usual three-winding transformers 1 and 2. It will be understood that the transmission lines L and L, may include one-way repeaters located either at the terminal stations, or at intermediate stations for the purpose of securing thedesired amplification. In order to simplify the diagram the one-way repeaters have been omitted. Re lays 3, at. 5 and 6 are provided whereby the ends of the transmission lines L, and L, may be disconnected from the terminating arrangements and interconnected through conductors 'l' at station C, and through a transmission arrangement at station D, here shown as comprising an amplifier A The amplifier it, may be adjusted so that its transmission equivalent is opposite in sign and equalto twice that to which it is desired to have each side of the four-wire circuit, exclusive of the terminal arrangements, adjusted. ln order to control the adjustment or" the four-wire circuits, amplifiers A, and A, are inserted in the lines L, and L, and the amplification of these amplifiers is determined by potentiometers P and The settingor the potentiometers is controlled by an automatic switch including wipers 5%,, S, and 5,. This switch is capable of movement in one direction only, and may be advanced step by step under the control of a stepping magnet 8. An alternating current relay i is provided, said relay having two sets of windings, one set being bridged across the connection including the amplifier A, and the other set of windings being in series with a local source oi current 9. A switch 10 is shown for the purpose of initiating the adjustment of the four-wire circuit. said switch being either hand operated, or else controlled by a suitable timing device. The circuits are so arranged that when the switch 10 is operated, the four-wire circuit is disconnected from the terminal arrangements and the ends of the lines L and L are interconnected as above described through the amplifier A The switch S then automatically steps around to its initial or zero position, thereby setting the potentiometers P, and P, so that the highest degree of amplification is produced by the amplifiers A and A, and singing takes place in the circuit. The relay V is designed to respond to singing oscillations and the switch again begins to ad vance under the control of this relay until singing ust ceases, when the relay no longer responds, and the switch remains in its advanced position with the potentiometer so set that each side of the four-wire circuit,

aside from its terminating arrangements, has a transmission equivalent opposite in sign and equal to one-hall that of the amplifier A Upon operating the switch 10, a circuit is completed through the winding of relay 11, which is thereby energized and is locked up over a circuit from ground. back contact cf the armature of relay 12, lowerfront contact of relay 11, and through the winding of said relay to battery. At its upper front contact relay 11 closes an interrupted circuit from ground over said contact, over the back contact of stepping magnet 8 and through the winding of said magnet to battery. The stepping magnet 8 now intermittently interrupts its own circuit, and under the control of relay 11 drives the switch S in the direction of the arrows until the wiper S encounters av grounded contact. A circuit is now closed from ground over the wiper S, and through the upper winding of relay 12 to battery. Relay 12 is now energized and by attracting its armature, opens the locking circuit of the relay 11, which is restored to normal, thereby opening the selfinterrupting circuit of stepping magnet 8 andstopping the rotation of switch S. Relay 12 at its front contact closes a circuit from ground, over the conductor 13, through the windings of relays at and 5, over conductor l l, over the two sides of the line la, in parallel, and thence through the windings of relays 6 and 3 to battery. The energization of relays 3, a, 5 and 6 disconnects the ends of the transmission lines L and la, from the terminating arrangements and interconnects them through conductors 7, and through the amplifier A The wiper S, of the switch S encounters a grounded contact at a position of the switch such that the wipers S and S, are connected to the extreme left hand contacts of the potentiometers P and P With this setting of the potentiometers, amplifiers A, and A, produce the highestdegree of amplification, and singing takes place in the circuit. The relay V now responds in a well known manner to the singlngoscillations and opens the normally closed circuit of relay 15. At its lower back contact, relay 15 now closes a locking circuit through the lower winding of the relay 12, so that the relays 3, 4, 5 and 6 are maintained in energized condition. At its upper back contact relay 15 closes a circuit from. ground, through the interrupter 16, and through the winding of the stepping magnet 8 to battery. It will be seen that this circuit is in dependent of the self-interrupting circuit previously traced for the stepping magnet 8, so that the stepping magnet now advances the switch S under the control of the interrupter 16. As the wipers S and S of the switch in advancing vary the setting of the potentiometer, the amplification of amplifiers A, and A, is gradually reduced until singing just ceases, whereupon the relay V, being no longer actuated, permits the circuit of relay 15 to be again closed. Relay 15 opens the circuit of stepping magnet 8 at its upper front contact, and stops the switch, while at its lower contact it opens the locking circuit through the lower winding of relay 12. In the meantime, the wiper of switch S has been advanced to an ungrounded contact so that the circuit through the upper winding of the relay 12 is open and said relay is tie-energized, thereby opening the circuit through relays 3, 4:, 5 and 6. The de-energization of these relays restores the four-wire circuit to its normal talking condition, and the potentiometers remain set in their adjusted position so that if the amplifier A, has been properly calibrated, the four-wire circuit will have the desired transmission equivalent.

A somewhat more refined arrangement is illustrated in Figure 2. This arrangement dillers from that of Figure 1 in that the amplifiers A, and A with the associated potentiometers and the switch S, are located at an intermediate station E, instead of at a terminating. station, the terminating station D is not shown, but is quite similarto that shown-tor station C. At the station C the ends of the lines D, and L, may be disconnected from the terminal arrangements, and connected through con- -ductors 7, which may include a transmission arrangement M in a similar manner the ends of the transmission lines L, and L, at station D (not shown) may be disconnected from the terminal arrangements, and connected through a similar transmission device. In either case, the transmission equivalent of these devices should be equal to, but opposite in sign to, that desired forthe tour-wire circuit. At station C the fourwire circuitis associated by means of a transformer 1 with a jack J adapted to'cooperate with a plug P whereby it may be connected to a terminating two-wire line. A similar arrangement will be provided at the other terminal station. Tlfe amplifier A in this form of the invention is not used to determine the transmission equivalent of the tour-wire circuit, since it is simply,

bridged across one of the transmission lines of the four-wire circuit through a transformer 17 at the intermediate station. E. The impedance of the bridge through transformer 17 should be very high, so that no appreciable transmission loss is involved by this connection. The switch S may be pro vided with an additional wiper for controlling signal lamps 18 and 19, when the setting ot the potentiometer indicates an abnormal condition of the circuit.

Normally a circuit is completed from the positive pole of the battery 20 over the back contact of relay 21, through the winding of relay 22, over the two sides of the line L,, and thence over a conductor 28, upper normal contact of relay 24, conductor 25,

The apparatus at through the winding of relay 26, and thence in parallel over the two sides of the transof similar relays at station D is maintained inthe same condition. When, however, the plug P is inserted in the jack J, in completing a connection to a terminating two-wire line, the sleeve relay 2? is energized and completes a circuit for the relay 21. The

relay 21 disconnects positive battery 20 from the simplex circuit through relays 22, 26 and the corresponding relay at station D, so that these relays are ole-energized. Similarly when the plug at station D corresponding to k g 1 1 is inserted in the jack-at that station the sleeve relay is energized to de-energize the relay corresponding to relay 21 and disconnect the negative battery. Thus it will be noted that the insertion of the. plug at either station will result in the deenergization of relays -22, 26-and relay at station D, corresponding to 22. Similarly relays at other intermediate stations corresponding to relay 26 will be deenergized. It will be noted that when the relay 22 is de-energized a circuit will be completed from ground through the windings of relays 3 and 6, over the back contact of relay 22, through the winding of said relay and over the simplex circuit previously traced to the negative battery at station D. The resistance of the line L, is so great, however, that relays 22, 26 and the corresponding relay at station D are only energized when both Morse batteries are connected in series. Relays 3 and 6 are also unenergized at this time due to the resistance of the line. As soon as relay 26 at station E is do -energized, a circuit is'completed from ground over its back contact and through the winding the slow releasing relay 28, which at its upper front contact connects battery to the filament circuit of amplifiers A A and A thereby rendering these amplifiers operative. The corresponding relays at other intermediate stations render the entire four-wire circuit operative as soon as the plug is inserted inthe jack at either terminal station. As sohn as the operator at station D has completed the connection to a terminal two-wire line at that station, telephonic transmission may take place.

At the close of the conversation, the plug P is withdrawn from the jack J, at station C, andthe similar plug withdrawn at station D. Relays 27 and 21 at station D are now (lo-energized, and similar relays at the nin other terminal station are also de-energized. Consequently the simplex circuit previously traced through relays 22 and 26 is again completed over the contact of relay 21 and its corresponding relay at station D, with both Morse batteries inseries. Relays 22, 26 and the corresponding relay at station D are again energized. Relay 26, which is quick acting, thereupon attracts its armature and completes a circuit from ground over its front-contact and over the lower front contact of slow acting relay 28, over the back contact of slow acting relay 29 and through the winding of relay 30 to battery. Relay 30 is now energized. and at its upper front contact, completes a locking circuit over the back contact of relay 24 to ground. At its lower front contact it completes a circuit from ground over the lower back contact of relay 24:, lower front contact of relay 30, interupt-ing contact of stepping magnet 8, and through the winding of said magnet to battery. Stepping magnet 8 now intermittently interrupts its own circuit and advances the switch S step by step until the wiper S engages a grounded contact, whereupon a circuitis completed from ground over the wiper S, and through the winding of relay 24 to battery. Relay 24Yat its lower contact opens the locking circuit of the relay 30, which is now restored to normal, and also opens the self-interrupting circuit just traced for the stepping magnet 8 thus stopping the rotation of switch S. Relay 24 at its lower front contact completes a circuit for the slow release relay 29, which holds open the initial energizing circuit of the relay 30 to prevent the energization of the said relay 3O due'to any further action of the relay 26. Relay 24 at its upper contact opens the simplex circuit, including the windings of relays 22, 26 and the corresponding relay at station D, so that these relays are again de-energized. A. circuit is now completed from the positive battery 20 at station C over the back contact of relay 22 and through the winding of relays 6 and 3 to ground. Relays 6 and 3 are now energized and disconnect the four-wire circuit from the terminal arrangements and interconnect the ends of lines L, and L, through the transmission device M In a similar manner the relays corresponding to relays 3 and 6 at station D are energized from the negative battery at said station, over the b-ackcontact of the relay corresponding to relay 22 at said station. Consequently the ends of the transmission lines L and L, at station D are interconnected in a similar manner.

The relay 26 upon being de-energized again completes the circuit of slow acting relay 28, which closes the filament heating circuits of amplifiers, A A, and 1A iVhen the wiper S, of the switch S engages a them again inoperative.

grounded contact, the switch i in such position that the po-tentiometers P and P, are set for the greatest amplification of amplifiers A and A Singing now takes place over the four-wire circuit, and the singing oscillations are transmitted through the trans-- former 17' and amplifier A, to the alternating current relay V, which is now actuated. Relay V opens the normally closed circuit through the relay 15, which is deenergized, and at its upper back contact closes a locking circuit for the relay 2%, which therefore continues to hold open the simplex circuit. Relay 15 at its lower back contact completes a circuit from ground through interrupter 16, and through the winding of stepping magnet S, which now advances the switch S gradually decreasing the amplification of amplifiers A and A, until singing just ceases. When singing ceases, relay V is no longer energized, and the circuit of relay 15 is again completed, thereby opening the circuit of the stepping magnet and stopping the switch S, and also opening the circuit of relay 24. Relay 24 upon being de-energized again completes the simplex circuit through relays 22 and 26 and the corresponding relay at station D. These relays are now energized, relay 22 functioning to open the circuit previously traced through the windings of relays 3 and 6. which are de-energized and again connect the ends of the transmission lines L and L, to the terminal arrangements. A similar action simultaneously takes place at the other terminal station. The relay 26, upon being again energized opens the circuit of the relay 28, which after a moment, is de-energized and opens the filament heating circuit for the amplifiers, rendering V The momentary circuit which would normally be closed over the front contact of relay 26, front contact of relay 28, through the winding of relay 30 is held open by the slow acting relay 29 until the relay 28 has had time to be deenergized. This prevents a false operation of the relay 30, which if operated, would disturb the setting of the potentiometers.

The switch S carries an additional wiper S which is so arranged that if it is nec essary to give an extremely high, or an extremely low setting to the potentiometer in order to secure the proper adjustment of the transmission circuit, said wiper S will close a circuit through one or the other of a pair of signaling lamps 18 or- 19, thereby indicating an abnormal condition of the circuit, which should receive especial attention. A relay 31 may be included in series with the lamps 18 and 19 to close a circuit to the pilot signal (not shown).

if the manual key 10 should be depressed and again relased, or if the contact 32, which is controlled by a suitable timing device, is opened and-closed, the relay 21 will be energized to open and again close the simplex circuit as alreadydescribed. This will result in the same'series of operations as has been set forth with reference to putting up and taking down a connection consequently the transmission equivalent of the four-wire circuit may be at any time regulated by simply pressing the key 10,,

mission lines, an automatic switch having a normal position and capable of movement in one direction only, means under the control of said switch for determining the amplification of said amplifiers, means to interconnect the ends of said transmission lines and to thereupon advance the switch from an abnormal position to its normal position, thereby setting said amplifying means for the highest degree of amplification so that singing takes place over the circuit formed by the interconnected pair of transmission lines, and means responsive to the singing thereby produced for advancing said switch until singing just ceases.

In a signaling system, a four-wire transmission circuit including a pair of transmission lines for transmitting in opposite directions, amplifiers for said transmission lines, an automatic switch having a normal position and capable of movement in one direction only, means under the control of said switch for determining the amplification of said amplifiers, means to interconnect the ends of said transmission lines, means responsive to such interconnection for automatically advancing said switch until its normal position is reached, thereby setting said amplifying means for the highest degree of amplification so that singing takes place over the circuit formed by the interconnected pair of transmission lines, means responsive to the singing thereby produced, means operative in the normal position of the switch to shift the control of its further advancement to said singing responsive means, whereby the switch is again advanced until singing just ceases.

8. In a signaling system, a four-wire transmission circuit interconnecting two ten minal stations and including a pair of transmission circuits for transmitting in opposite directions between said stations; normally inoperative amplifying means for said transmission lines located at an intermediate station, means controllable from a terminal stat-ion to render said amplifying means operative and to interconnect the ends of said pair of transmission lines, means to in crease the amplification of said amplifying means so that singing takes place over the circuit thus formed, and means located at the intermediate station and responsive to the singing thus produced for gradually decreasing the amplification until singing just ceases. I

4. In a signaling system, a four-wire transmission circuit interconnecting two terminal stations and including a pair of transmission lines for transmitting in opposite directions between said stations, normally inoperative amplifying means for said trans mission lines located at an intermediate station, means controllable from a terminal station to render said amplifying means operative and to interconnect the ends of said pair of transmission lines, means responsive to the interconnection of said lines to increase the amplification of said amplifying means so that-singing takes place over the circuit thus formed, and means located at the intermediate stations and responsive to the singing thus produced for gradually reduc ing the amplification until singing just ceases.

5 In a signaling system, a four-wire transmission circuit'interconnecting two terminal stations and including a pair of transmission lines for transmitting in opposite directions, normally inoperative amplifying means for said transmission lines at an intermediate station, means at said terminal station to associate said four-wire circuit with terminating two-wire lines, means responsive to such associations'to render said amplifying means operative, means responsive to the disconnection of the terminating two-wire lines from the four-Wire circuit to interconnect the ends of said pair of trans mission lines and to increase the amplification of the amplifying means so that singing takes place over the circuit thus formed, and means responsive to the singing thus produced for gradually decreasing the amplification of said amplifiers until singing just ceases.

6. In a signaling system, a four-wire transmission circuit interconnecting two terminal stations and including a pair of transmission lines for transmitting in opposite directions, means at a terminal station for connecting and disconnecting terminating two-wire lines to said four-wire circuit, means responsive to the connection and subsequent disconnection of the four-wire cirgradually increase the loss until singing ust ceases.

7. In a signaling system, a transmission circuit for transmitting fluctuating signaling currents and including an adjustable transmission device, means operating automatically to adjust said transmission device in response to changes in the transmission condition of said transmission circuit so that the transmission circuit will have a predetermined transmission equivalent, and means to indicate an abnormal adjustment of said transmission device.

8. In a signaling system, a transmission circuit, signaling instruments for transmitting fluctuating signaling currents over said circuit, receiving instruments for receiving the signals thus transmitted, an adjustable transmission device in said transmission circuit, means functioning to periodically adjust said transmission device to compensate for variations in the transmission circuit so that the circuit when thus adjusted Will have a predetermined transmission equivalent, and means in addition to said signaling and receiving instruments to indicate an abnormal adjustment of said transmission circuit, thereby indicating an abnormal condition of some other part of the transmission circuit.

9. In a signaling system a transmission circuit, signaling instruments for transmitting fluctuating signaling currents over said circuit, receiving instruments for receiving the signals thus transmitted, a signaling circuit, a transmission device controlled over said signaling circuit for adjusting the transmission equivalent of the transmission circuit, and means in addition to said signaling and receiving instruments for indicating an abnormal condition of the transmission device.

10. In a signaling system a transmission circuit extending between two stations, a transmission device in said circuit which is normally inoperative to transmit current, a signaling circuit, means controllable over said signaling circuit from either station for-rendering said transmission device operative, and means controllable over said signaling circuit from either station to adjust the transmissionof said transmission device, and thereby adjust the transmission equivalent of said transmission circuit.

In testimony whereof, I have signed my name to this specification this 9th day of September 1918.

SAMUEL P. SHACKLETON. 

